Suggest `impl Trait` for References to Bare Trait in Function Header
Fixes#125139
This PR suggests `impl Trait` when `&Trait` is found as a function parameter type or return type. This makes use of existing diagnostics by adding `peel_refs()` when checking for type equality.
Additionaly, it makes a few other improvements:
1. Checks if functions inside impl blocks have bare trait in their headers.
2. Introduces a trait `NextLifetimeParamName` similar to the existing `NextTypeParamName` for suggesting a lifetime name. Also, abstracts out the common logic between the two trait impls.
### Related Issues
I ran into a bunch of related diagnostic issues but couldn't fix them within the scope of this PR. So, I have created the following issues:
1. [Misleading Suggestion when Returning a Reference to a Bare Trait from a Function](https://github.com/rust-lang/rust/issues/127689)
2. [Verbose Error When a Function Takes a Bare Trait as Parameter](https://github.com/rust-lang/rust/issues/127690)
3. [Incorrect Suggestion when Returning a Bare Trait from a Function](https://github.com/rust-lang/rust/issues/127691)
r? ```@estebank``` since you implemented #119148
Fix supertrait associated type unsoundness
### What?
Object safety allows us to name `Self::Assoc` associated types in certain positions if they come from our trait or one of our supertraits. When this check was implemented, I think it failed to consider that supertraits can have different args, and it was only checking def-id equality.
This is problematic, since we can sneak different implementations in by implementing `Supertrait<NotActuallyTheSupertraitSubsts>` for a `dyn` type. This can be used to implement an unsound transmute function. See the committed test.
### How do we fix it?
We consider the whole trait ref when checking for supertraits. Right now, this is implemented using equality *without* normalization. We erase regions since those don't affect trait selection.
This is a limitation that could theoretically affect code that should be accepted, but doesn't matter in practice -- there are 0 crater regression. We could make this check stronger, but I would be worried about cycle issues. I assume that most people are writing `Self::Assoc` so they don't really care about the trait ref being normalized.
---
### What is up w the stacked commit
This is built on top of https://github.com/rust-lang/rust/pull/122804 though that's really not related, it's just easier to make this modification with the changes to the object safety code that I did in that PR. The only thing is that PR may make this unsoundness slightly easier to abuse, since there are more positions that allow self-associated-types -- I am happy to stall that change until this PR merges.
---
Fixes#126079
r? lcnr
Go over all structured parser suggestions and make them verbose style.
When suggesting to add or remove delimiters, turn them into multiple suggestion parts.
Continue compilation after check_mod_type_wf errors
The ICEs fixed here were probably reachable through const eval gymnastics before, but now they are easily reachable without that, too.
The new errors are often bugfixes, where useful errors were missing, because they were reported after the early abort. In other cases sometimes they are just duplication of already emitted errors, which won't be user-visible due to deduplication.
fixes https://github.com/rust-lang/rust/issues/120860
```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
--> f100.rs:2:33
|
2 | let _ = std::mem::size_of::<[i32]>();
| ^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
--> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
|
312 | pub const fn size_of<T>() -> usize {
| ^ required by the implicit `Sized` requirement on this bound in `size_of`
```
Fix#120178.
Do not attempt to provide an accurate suggestion for `impl Trait`
in bare trait types when linting. Instead, only do the object
safety check when an E0782 is already going to be emitted in the
2021 edition.
Fix#120241.
Detect object safety errors when assoc type is missing
When an associated type with GATs isn't specified in a `dyn Trait`, emit an object safety error instead of only complaining about the missing associated type, as it will lead the user down a path of three different errors before letting them know that what they were trying to do is impossible to begin with.
Fix#103155.
When an associated type with GATs isn't specified in a `dyn Trait`, emit
an object safety error instead of only complaining about the missing
associated type, as it will lead the user down a path of three different
errors before letting them know that what they were trying to do is
impossible to begin with.
Fix#103155.
When we encounter a `dyn Trait` that isn't object safe, look for its
implementors. If there's one, mention using it directly If there are
less than 9, mention the possibility of creating a new enum and using
that instead.
Account for object unsafe `impl Trait on dyn Trait {}`. Make a
distinction between public and sealed traits.
Fix#80194.
On the following example, point at `String` instead of the whole type:
```
error[E0277]: the trait bound `String: Copy` is not satisfied
--> $DIR/own-bound-span.rs:14:24
|
LL | let _: <S as D>::P<String>;
| ^^^^^^ the trait `Copy` is not implemented for `String`
|
note: required by a bound in `D::P`
--> $DIR/own-bound-span.rs:4:15
|
LL | type P<T: Copy>;
| ^^^^ required by this bound in `D::P`
```
